The purpose of this project is an examination of the role of proline in glucose metabolism by Pepostreptococcus anaerobius ATCC 27337. Resting cells of P. anaerobius were shown to have an absolute requirement for low concentrations of L.-proline in order to utilize glucose. The requirement was shown to reside at the level of initial transport of the sugar into the cell: no accumulation of radiolabelled glucose occurs in resting cells until the addition to the reaction vessel of the imino acid. The action of proline on sugar transport is proposed to occur via the activation of the metabolism of an endogenous reserve of amino acids, notably alanine, within the cell. The reduction of proline to -amino valeric acid allows for the removal of reducing equivalents generated from the oxidation of the endogenous amino acid pool. The metabolism of these amino acids gives rise to the formation of a phosphoryl donor for the sugar phosphotransferase system which can then transport into the cell the extracellular sugar. These studies have thereby demonstrated a unique interelationship of sugar transport and amino acid metabolism. That each of these processes is dependent on an exogenous source of proline reflects the relationship that exists between the oral peptostreptococci and the high proline rich proteins of their natural habitat.